The present invention relates to a fiber optic link continuity check for single and multi-cable systems.
Transmission of information over long distances using fiber optic cables requires that powerful optical sources be used, such as laser diodes. If misused, the optical lightwave radiation from some of the more powerful optic sources can cause eye damage. While Class One laser diodes are considered safe for fiber optic link users if structured work practices are used, an uninformed user could be endangered, particularly if collimating optics, such as a magnifier, are used to view the output lightwave. Obviously, this can only occur if the fiber optic link is "open" at some point, i.e. a link discontinuity has occurred.
This optical radiation endangerment can occur if someone disconnects the wrong fiber optic cable and assumes that this cable is connected to a laser source that has been turned off. Since minute contaminants, such as sandy grit, can prevent proper coupling of a fiber optic cable to its mating connector, it is not altogether unlikely that uninformed personnel might well consider using a magnifier to look for such contaminants.
The transmission of information over a fiber optic link depends on link closure, i.e. all link elements must be in place from source to receiver. Presently, the only test to check that fiber optic link is capable of successfully transmitting information is to "try it out". If the link is a single fiber optic cable, this requires that another link (telephone cable, radio signal, or a second fiber optic cable) is used to bring the "O.K., I got the information" signal back to the information source point to determine that the link is, in fact, working properly. When several fiber optic links are connected between the first ("source") and second ("receiver") locations, this is very practical. But, when only a single fiber connects the two locations, this "backhaul" information link can be troublesome to arrange.
From the personnel safety standpoint, providing the "O.K., its working" signal (versus a "Danger, link may be open" signal) over the backhaul link may not protect a careless person, since the backhaul data monitor line may not act quickly enough to prevent harmful radiation from a powerful source emerging to damage a person's eye.
Necessarily, the backhaul line must detect the lack of information coming over the main fiber optic link so as to alarm the system supervisor that the monitored link is, in fact, open unexpectedly. If the main fiber optic link is being used to transmit data on an intermittent basis, this monitoring can be difficult.